Faculty Publications
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Item Dual colorimetric receptor with logic gate operations: Anion induced solvatochromism(Royal Society of Chemistry, 2014) Kigga, M.; Swathi, N.; Manjunatha, J.R.; Das, U.K.; Nityananda Shetty, A.N.; Trivedi, D.R.A receptor R1 was designed and synthesised for colorimetric detection of F- ions as well as Cu2+ ions via intramolecular charge transfer mechanism. Upon addition of F- ions in dry DMSO, the color of the receptor R1 changed from pale yellow to blue. The receptor showed a unique property of solvatochromism by displaying different coloration with different solvents only in the presence of F- ions, which were applied to determine the percentage composition of binary solvent mixtures. The receptor R1 was able to detect Cu2+ ions colorimetrically where it exhibited a color change from pale yellow to orange-red. In addition, the receptor was subjected to molecular logic gate applications, wherein it showed 'ON-OFF' switching operations. © 2014 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Pharmaceutical salts of ethionamide with GRAS counter ion donors to enhance the solubility(Elsevier B.V., 2017) Nechipadappu, S.K.; Trivedi, D.R.Pharmaceutical salts of BCS class II second line anti-tuberculosis drug ethionamide (ETH) with various counter ions namely, 2-chloro-4-nitrobenzoic acid (CNB), 2,6-dihydroxybenzoic acid (2,6HBA), 2,3-dihydroxybenzoic acid (2,3HBA) and 2,4-dinitrobenzoic acid (DNB) were synthesized by crystal engineering approach. All the synthesized salts were characterized by various spectroscopic (NMR, FT-IR,), thermal (DSC & TGA) and PXRD techniques. The crystal structure of the synthesized salts was determined by single-crystal X-ray diffraction techniques. All the reported salts, except ETH-2,3HBA exhibited charge assisted acid pyridine heterosynthon. In ETH-2,3HBA hydoxyl pyridine heterosynthon is observed. In ETH-CNB salt, both ionic and neutral acid pyridine heterosynthon were observed in the asymmetric unit. ETH-DNB salt consists of both partial and complete proton transfer from DNB to ETH in the asymmetric unit. All the synthesized salts were found to be non-hygroscopic at accelerated humid condition (~ 75% RH). Solubility experiment has been performed in purified water and in 0.1 N HCl (pH = 1) solution and found that the solubility of ETH-CNB salt was about eight-fold higher soluble than ETH in purified water. The solubility of synthesized salts follows the order of ETH < ETH-2,3HBA < ETH-2,6HBA < ETH-CNB in purified water. © 2016 Elsevier B.V.Item A new colorimetric chemosensors for Cu2+ and Cd2+ ions detection: Application in environmental water samples and analytical method validation(Elsevier B.V., 2017) Tekuri, V.; Trivedi, D.R.A new heterocyclic thiophene-2-caboxylic acid hydrazide based chemosensor R1 to R4 were designed, synthesized and characterized by various spectroscopic techniques like FT-IR, UV-Vis, 1H NMR, 13C NMR, Mass and SC-XRD. The chemosensor R3 showed a significant color change from colorless to yellow in the presence of Cu2+ ions and chemosensor R4 showed a significant color change from colorless to yellow in the presence of Cd2+ ions over the other tested cations such as Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+, Ag2+, Al3+, Pb2+, Hg2+, K+, Ca2+ and Mg2+. The high selective and sensitivity of R3 towards Cu2+ and R4 towards Cd2+ ions was confirmed by UV-Vis spectroscopic study. The R3 showed a red shift in the presence of Cu2+ ions by ??max 67 nm and R4 showed a red shift in the presence of Cd2+ ions by ??max 105 nm in the absorption spectrum. The binding stoichiometric ratio of the complex between R3 - Cu2+ and R4 - Cd2+ ions have been found to be 1:1 using the B-H plot. Under optimized experimental conditions, the R3 and R4 exhibits a dynamic linear absorption response range, from 0 to 50 ?M for Cu2+ ions and 0 to 30 ?M for Cd2+ ions, with the detection limit of 2.8 × 10?6 M for Cu2+ and 2.0 × 10?7 M for Cd2+ ions. The proposed analytical method for the quantitative determination of Cu2+ and Cd2+ ions was validated and successfully applied for the environmental samples with good precision and accuracy. © 2017 Elsevier B.V.Item Synthesis of cocrystals/salts of flucytosine: Structure and stability(Royal Society of Chemistry, 2018) Nechipadappu, S.K.; Ramachandran, J.; Naveen, N.; Lokanath, N.K.; Trivedi, D.R.5-Fluorocytosine or flucytosine (FLC) is a well-known drug for anti-fungal treatment and is one of the essential medicines needed in a health system. The main disadvantage of FLC drugs is their instability due to hydration under storage conditions. In the present work, cocrystal/salt screening experiments resulted in three molecular salts of FLC with dihydroxybenzoic acid derivatives, 2,3-dihydroxybenzoic acid (2,3HBA), 3,5-dihydroxybenzoic acid (3,5HBA), and 2,6-dihydroxybenzoic acid (2,6HBA), and two cocrystals with gallic acid (GAA) and glutaric acid (GLA). Since FLC drugs are highly susceptible to hydration, the present work concentrated on the stability of the synthesized molecular salts/cocrystals under different relative humidity (RH) conditions. All the newly formed crystalline adducts were characterized structurally, and the crystal structures were determined using single-crystal X-ray diffraction techniques (SCXRD). The FLC-2,6HBA salt was found to be a monohydrate, whereas the FLC-3,5HBA salt was crystallized as a hemipentahydrate. FLC-2,3HBA and FLC-GLA were crystallized in 2:1 equimolar ratios of FLC and the coformer. The FLC-GAA cocrystal crystallized in a 1:1 equimolar ratio. Two point heterosynthons between FLC and the coformer were observed in all the crystalline structures except FLC-GLA, where the structure was formed through a single point heterosynthon. Stability studies under different relative humidity conditions showed the non-hygroscopicity of the synthesized molecular salts/cocrystals. It was found that the FLC-2,3HBA salt, and the FLC-GAA and FLC-GLA cocrystals did not experience any hydration under the accelerated humidity conditions (both 70-75% RH and 90-95% RH) at ambient temperature (?30 °C). However, FLC-2,6HBA and FLC-3,5HBA were found to be hygroscopic under 70-75% RH conditions. Furthermore, all the synthesized salts/cocrystals except FLC-3,5HBA were found to be stable for 2 months under ambient conditions (?30 °C, 60-65% RH). Therefore, the FLC-2,3HBA salt, and the FLC-GAA and FLC-GLA cocrystals are better candidates for the preparation of new drug products of FLC. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Colorimetric and fluorometric turn-on sensor for selective detection of fluoride ions: Sol-gel transition studies and theoretical insights(Royal Society of Chemistry, 2018) Pangannaya, S.; Mohan, M.; Trivedi, D.R.A new organic receptor R1 based on a naphthyl unit covalently linked to a long alkyl chain has been designed, synthesized and characterized by standard spectroscopic techniques. The colorimetric response of receptor R1 from colorless to a pale yellow color and blue fluorescence emission in the presence of F- ions revealed its selective sensing ability in the solution phase. UV-Vis titration, fluorescence titration and 1H NMR titration studies confirmed the formation of the R1-F- complex. Receptor R1 formed a stable gel in DMSO and was confirmed through the standard heating-and-cooling method. Addition of F- ions resulted in disruption of the gel forming a solution that exhibited blue fluorescence emission. The binding constant of the R1-F- complex was found to be of the order of 5.9 × 105 M-1. DFT studies revealed the formation of the receptor-anion complex agreeing well with the experimental results. The detection limit was calculated and found to be 0.8 ppm, implying the potential for application of receptor R1 in environmental applications. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Photophysics of proton transfer in hydrazides: A combined theoretical and experimental analysis towards OLED device application(Royal Society of Chemistry, 2019) Mohan, M.; Satyanarayan, M.N.; Trivedi, D.R.Hydrazides generate phototautomers and thus, a mechanistic interpretation to uncover the excited state dynamics of such systems is highly necessary to theorize principles based on experimental speculations. Accordingly, focus on the proton transfer barrier, which is a questionable step-wise or hypothetical simultaneous double proton transfer on structurally favored species, is quintessential; however, to the best of our knowledge, theoretical insights into such findings remain rare. Thus, TX, PX and FX (where X = 2 and 3) were designed and synthesized by incorporating hydrazides, which exhibit the phenomenon of excited state intramolecular proton transfer (ESIPT). Some of the molecules exhibited electroluminescence when employed as an active emitter material in fabricated OLED devices. Theoretical predictions support the presence of extended conjugation in TX, PX and FX (where X = 2 and 3) to support ESIPT efficiently in comparison with TX, PX and FX (where X = 1). The solvatochromic study revealed that TX, PX and FX (where X = 2 and 3) exhibit a distinct double peak in THF solvent, characteristic of ESIPT. Interestingly, for some of the molecules, emission in thin film form showed a double peak, which indicates ESIPT in the solid state. However, it was found that aggregation induced emission (AIE) was inactive in these molecules. The geometrical attributes of the molecules and the nature of electronic orbital distribution well underline the principle supporting excited state proton translocation. The theoretically estimated energy transitions exhibited good correlation with the experimental results. Also, the potential energy scans revealed the molecules possess a lower forward barrier at their excited state in comparison with that of their ground state, promoting ESIPT. The potential energy surface scans performed on structurally favored species confirmed the impossible double proton transfer and highly difficult step-wise double proton transfer. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.